The invention relates in general to fluid stop valves and, more specifically, stop valves for hydraulic lift systems.
Hydraulic lift systems are common in many industrial applications. By way of example, many truck units employ one or more hydraulic cylinders for the purpose of elevating and lowering a truck bed. In such applications, a trailer is generally coupled to a tractor and includes a bed, or other hydraulic superstructure, that can be raised or lowered. It is common to carry loose material within the bed such as gravel or earth. The bed is pivotally coupled to the trailer frame at a rearward location. One hydraulic cylinder or, as is more typical, a system of telescopic hydraulic cylinders is mounted to a forward end of the trailer, below a forward end of the trailer bed. Hydraulic fluid is pumped from the tractor into the hydraulic cylinders to cause the cylinders to extend and raise the forward end of the trailer bed. Once raised, the trailer is readily emptied of its contents. Thereafter, the operator of the unit causes hydraulic pressure to be gradually withdrawn from the lift cylinders and the cylinders slowly retract, lowering the bed of the trailer.
The user activates the hydraulic lift system from the cab of the tractor or from an exterior location, depending upon the design of the lift. Hydraulic fluid is highly pressurized and directed to the lift cylinders by appropriate flexible conduits. The conduits or hoses, typically formed of rubber or composite materials, are routed from the pump unit, along the trailer chassis, and to the lift cylinder(s). The route followed by the flexible hydraulic hoses is typically non-linear and includes several bends or elbows. These bends or elbows, however, represent constrictions where breakage of the high pressure line can, and frequently does, occur. Moreover, breakage generally occurs when the line is in the high pressure mode; that is, when the bed is raised and the lift cylinders fully extended.
Breakage in the hydraulic line at or near the lift cylinders causes immediate expulsion of the pressurized hydraulic oil to the ground or upon the equipment. In addition to creating an environmental event requiring extensive clean up, the expulsion of the pressurized hydraulic fluid causes an immediate loss of pressure to the lift system. If the breakage occurs while the cylinders are extended and the bed elevated, the lift cylinders will retract immediately, rather than gradually, and the bed of the trailer will precipitously fall. The falling bed can destabilize and tip the tractor and trailer over, causing considerable damage to the trailer and/or tractor. More importantly, a freefalling bed can pose a risk of bodily injury to surrounding individuals or the operator of the unit. The operator, stationed at the controls for the hydraulic system, will generally observe a breakage in the hydraulic line to the lift cylinders. However, even if a breakage is detected, the operator is powerless to prevent the resultant sudden failure of the lift system and consequent rapid collapse of the elevated bed.
A preventative stop valve system, accordingly, is needed in the industry to prevent a precipitous loss of hydraulic fluid from a lift system in the event rupture of hydraulic lines occur. Such a stop valve would be useful if positioned in the hydraulic system so as to stop rapid expulsion of hydraulic fluid from the lift cylinders in the event the hydraulic lines rupture. The valve, however, to be effective, must operate quickly to stem the outflow of hydraulic oil. The valve should further be of reliable construction, be convenient to activate, and operate predictably when needed to effectively abate the loss of fluid. In addition, because of the large number of lift units already in use, a suitable preventative stop valve system should be capable of retrofit implementation into existing lift units with a minimum level of inconvenience and expense. Achievement of a suitable valve system would prevent a catastrophic collapse of the lift system and eliminate consequential damage to property and injury to personnel.
It is, therefore, an object of the invention to provide a preventative stop valve system for hydraulic lift units that prevents a precipitous loss of hydraulic fluid in the event rupture of hydraulic lines occurs.
A further object of the invention is to provide a preventative stop valve system that operates quickly to stem the outflow of hydraulic oil in the event that a rupture of hydraulic lines occurs.
Another object of the invention is to provide a preventative stop valve system that is capable of retrofit implementation into existing lift units with a minimum level of inconvenience and expense.
Still further, it is an object of the invention is to provide a preventative stop valve system that is of reliable construction, convenient to activate, and operates predictably when needed to effectively abate the loss of fluid.
Yet another object of the invention is to provide a preventative stop valve system that self-tests responsive to normal operation of a tractor-trailer unit.
An additional object of the invention is to provide a stop valve system for a trailer lift unit having an override mechanism for allowing use of the lift unit when the trailer is decoupled from a tractor.
An ancillary object of the invention is to provide a preventative stop valve system for a trailer lift unit compatible with existing user-operated controls for the trailer.
A further object of the invention is to provide a method of retrofitting existing trailers with a preventative stop valve system that operates quickly to stem the outflow of hydraulic oil in the event that a rupture of hydraulic lines occurs.
These and other objects, which will be apparent to one skilled in the art, are achieved by a preferred embodiment described below. The preventative stop valve system comprises a stop valve interposed in the hydraulic line of a trailer lift unit. The valve includes an elongate housing having an internal chamber and intake and outlet fluid portals extending through sidewalls of the housing and establishing with the internal chamber a fluid flow path. A piston member is reciprocally moveable within the chamber between an open and closed position. In the closed position, the piston obstructs the fluid flow path while, in the open position, the piston permits fluid to flow through the housing chamber. A spring member biases the piston in the closed position. The housing further includes an air intake portal in one end connected to the air brakes of the trailer. High pressure at the intake portal, a consequence of setting the trailer air brakes, is necessary to override the spring member and open the valve. Release of the air pressure to the brakes, typically from the cab of the tractor, drops the air pressure at the valve air intake portal and causes the valve to close. The switch used to release the brakes can thus be activated by the user to close the valve and stop the release of hydraulic oil in the event that a rupture in the hydraulic lines is detected. An override arm is further provided to allow activation of the stop valve with the trailer decoupled from its associate tractor. The override arm accordingly allows the valve to be opened and the lift unit raised when the brake system of the trailer is decoupled from the tractor.
For the benefit of existing tractor-trailer units, a method of retrofitting existing units with a preventative stop valve system is provided. The method comprises the steps of: a.) connecting a stop valve housing in the hydraulic line, the housing including an air intake portal at one end; an elongate piston seated within a central chamber of the housing and reciprocally moveable within the chamber responsive to a drop in air pressure at the air intake portal between an open position and a closed position, the piston obstructing the flow of fluid through the housing in the closed position and allowing the flow of fluid through the housing in the open position; b.) connecting the air intake portal of the valve housing to the trailer brake air line; and c.) selectively releasing the brakes of the tractor-trailer to cause a drop in air pressure at the air intake portal of the stop valve and consequently move the piston into the closed position.